The wavelength dependence of photoproduct formation and quantum yields was evaluated for fluorinated pesticides and pharmaceuticals using UV-light emitting diodes (LEDs) with 255, 275, 308, 365, and 405 nm peak wavelengths. The fluorinated compounds chosen were saflufenacil, penoxsulam, sulfoxaflor, fluoxetine, 4-nitro-3-trifluoromethylphenol (TFM), florasulam, voriconazole, and favipiravir, covering key fluorine motifs (benzylic-CF3, heteroaromatic-CF3, aryl-F, and heteroaromatic-F). Quantum yields for the compounds were consistently higher for UV-C as compared to UV-A wavelengths and did not show the same trend as molar absorptivity. For all compounds except favipiravir and TFM, the fastest degradation was observed using 255 or 275 nm light, despite the low power of the LEDs. Using quantitative 19F NMR, fluoride, trifluoroacetate, and additional fluorinated byproducts were tracked and quantified. Trifluoroacetate was observed for both Ar-CF3 and Het-CF3 motifs and increased at longer wavelengths for Het-CF3. Fluoride formation from Het-CF3 was significantly lower as compared to other motifs. Ar-F and Het-F motifs readily formed fluoride at all wavelengths. For Het-CF3 and some Ar-CF3 motifs, 365 nm light produced either a greater number of or different major products. Aliphatic-CF2/CF3 products were stable under all wavelengths. These results assist in selecting the most efficient wavelengths for UV-LED degradation and informing future design of fluorinated compounds.
Bibliographical noteFunding Information:
Funding for this project was provided by a graduate fellowship to A.B. from the University of Minnesota College of Science and Engineering, the Minnesota Environment and Natural Resources Trust Fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR), and the Joseph T. and Rose S. Ling Professorship. Thanks are offered to Jamie Lom for help with sampling the photolysis experiments. We thank the Minnesota NMR Center for access to instrumentation. Funding for NMR instrumentation was provided by the Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation. Thanks are offered to Peter Villalta and Yingchun Zhao at the Analytical Biochemistry Mass Spectrometry Services Shared Resource at the Masonic Cancer Center, University of Minnesota, for help with LC–HRMS instrumentation.
© 2023 American Chemical Society.
- F NMR
- quantum yield
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.
- Research Support, Non-U.S. Gov't
- Research Support, N.I.H., Extramural